1. Field of the Invention
The present invention relates to an alternating current (AC) light-emitting diode (LED) lamp and more particularly to an AC LED lamp adaptive to ambient luminance.
2. Description of the Related Art
Lamps are indispensable electronic appliances required for lighting in human daily life. The march of technological progress has driven manufacturers to launch lamps with multi-stage dimmer adjustment in the market so that users can adjust luminance of the lamps according to environmental luminance. What's more, an automatic luminance-adjusting lamp is designed so that lighting luminance can be automatically adjusted according to ambient luminance to enhance power-saving effect.
With reference to FIG. 6, an automatic luminance-adjusting lamp has a luminance sensor 62 externally mounted thereon for a driving circuit 61 of the lamp to receive sensing signals of the luminance sensor 62, and determine and adjust luminance of the lamp. As regular lamps are always lit after being turned on, the luminance sensor must be positioned away from the lamp shells of the lamps to only receive the ambient luminance of the lamp. Hence, the luminance sensor 62 is mounted on an outer periphery of a lamp shell 60 and is located at a position not easily affected by light emitted by the lamp, such as on a top of the outer periphery of the lamp shell. However, besides a compromise of its aesthetic appeal, the lamp with such arrangement is still affected by the ambient luminance fails to provide accurate luminance in response to the ambient luminance.
With reference to FIG. 7, another automatic luminance-adjusting lamp is shown. To more accurately sense ambient luminance of the lamp and not to be affected by light emitted by the lamp, the lamp has an extension circuit 63 and a luminance sensor 62. The extension circuit 63 is externally connected to an outer periphery of the lamp. One terminal of the luminance sensor 62 is connected to the extension circuit 63 so that the luminance sensor 62 can be positioned away from the lamp to acquire more accurate ambient luminance.
No matter which one of the foregoing arrangements of the luminance sensor is chosen, the tradeoff of enhancing accuracy in sensing ambient luminance creates a complicated lamp structure. For a replaceable bulb, the complicated lamp structure is redundant and lowers customers' willingness to purchase. With reference to FIG. 8, dedicated to regular replaceable bulbs, a small lampshade 621 is mounted on a bottom of the lamp shell to fix the luminance sensor 62 therein so that the luminance sensor 621 can accurately sense the ambient luminance even though the lamp is lit. Likewise, the lamp with such arrangement also compromises the aesthetic appeal of the lamp and creates shadow as a result of the blockage of the small lampshade 621 to lessen original lighting of the lamp.
Despite the power-saving effect, the lamps with the function of sensing ambient luminance fail to take factors of lighting and saving power into account.